1. Field of the Invention
The present invention pertains to switched resistor arrays, and in particular pertains to a system and method which significantly reduces switch error while permitting large impedances of the switches.
2. Description of the Prior Art
Applications for flat panel displays (active matrix, passive matrix, EL, . . . ) are growing. For example, active matrix displays can provide advantages over conventional LCD's in the areas of viewing angle, response time and information content. Military and commercial applications such as cockpit displays, mapping displays and imaging systems can utilize these features to create extremely accurate image reproductions.
A new generation of complex driver chips are required to implement these systems. For instance, there is a need for "next generation" IC's which can take full advantage of the capabilities of current and upcoming flat panel displays by providing extreme image accuracy. Such image accuracy is obtained at the expense of space. Space is a primary concern in applications using flat panel displays because the display driver IC chips will have thousands of connections between the driver chips and the display due to the large number of display driver chips required in these applications.
Current system architectures for LCD drivers employ both row and column driver IC's. These drivers are high speed chips having responsibility for accurate generation of large numbers of voltage levels used to drive the flat panel displays. These IC's need to be fast, handle large voltages, have a multitude of outputs, provide low offset error, contain tens of thousands of transistors, and yet minimize power. These conflicting design issues require careful analysis in the light of current IC technology.
For example, current flat panel active matrix display systems utilize digital-to-analog (D/A) converters which may require output offset voltages to be within a .+-.12 mv tolerance over a 12 volt output range. This is equivalent to approximately 10 bit D/A accuracy. Such accuracy is not available in the existing art without increased die sizes attributable to the large switches necessary to achieve that accuracy. The impedance of the switches used for selecting various voltages or resistors can be a design issue when extremely accurate output voltages are necessary. Prior applications requiring low switch losses have simply used large switches with small impedances. Increased die sizes however, are not an option due to the space limitations associated with flat panel display drivers. This invention allows flat panel display driver technology to achieve the necessary accuracy while simultaneously meeting the limited space requirements necessary to manufacture flat panel display drivers.